1. Field of the Invention
The present invention relates to baseband circuits and a technique for reducing power in such baseband circuits, especially when a linear regulator is used.
2. Related Art
Stacked devices are well-known in radio frequency (RF) circuits, wherein “stacked” devices are defined as devices that share the same current. For example, FIG. 1 illustrates known stacked RF circuits including a mixer 120 and a low noise amplifier (LNA) 121. LNA 121 receives a differential input signal, i.e. inp and inn, on the gates of transistors 107 and 115, respectively. Note that in this embodiment, the transistors in LNA 121 and mixer 120 are NMOS transistors.
In this embodiment of LNA 121, the sources of transistors 107 and 115 are coupled to a current source 108, which in turn is connected to ground. An inductor 106 is connected between the drain of transistor 107 and an intermediate voltage node 130. Similarly, an inductor 114 is connected between the drain of transistor 115 and intermediate voltage node 130. Capacitors 105 and 113 are respectively connected to the drains of transistors 107 and 115.
In this embodiment of mixer 120, the gates of transistors 104 and 112 are connected to capacitor 105 and 113, respectively. A transistor 104, a transistor 102, and an inductor 101 are connected in series between intermediate voltage node 130 and a voltage supply VDD. Similarly, a transistor 112, a transistor 110, and an inductor 109 are connected in series between intermediate voltage node 130 and the voltage supply VDD. Transistors 102 and 110 receive a negative local oscillator signal (LO−) on their gates. A transistor 103 is connected between the drain of transistor 104 and the drain of transistor 110. A transistor 111 is connected between the drain of transistor 112 and the drain of transistor 102. The gates of transistors 103 and 111 both receive a positive LO signal (LO+). In this embodiment, the outputs outp and outn of mixer 120 are provided at the drains of transistors 102 and 110.
In FIG. 1, the three transistors 102, 104, and 107, for example, may be easily stacked using a VDD voltage of 1.8 V. However, as devices in these RF circuits become smaller, the supply voltage must be decreased to minimize the possibility of device (i.e. transistor) failure. Unfortunately, the efficiency of the regulator providing the supply voltage may suffer when the output voltage decreases. Moreover, to have constant power with reduced voltage, current must be increased, thereby undesirably necessitating more chip area, e.g. trace area and/or device area.